Head scratcher

Re-fitted the cylinder head after new guides fitted. Connected everything up & checked valve clearences. Started on 3rd kick but only on 1 cylinder. Checked plug - no spark. After examining the wiring I found I had put a negative wire to a positive terminal on the coil on the side that was firing. Corrected this wire. Now both plugs sparking. Kicked for eternity with only backfiring from carbs & exhaust. Then lo & behold it started & ran for approximately 10 -15 seconds beautifully. It then just stopped running & no matter how many times I kick all I get is backfiring with the odd teaseing splutter. I noticed a loose spade in a block (2'' x 3/4'' housed behind the steering head - this has 2 spades coming out of it of which 2 black & white wires connect to) which duly fell off. However, am I right in thinking that this block is part of the old ignition system & is no longer required as it has boyer ignition fitted?
I still think its electrical although the symtoms are similar to fuel starvation. I am flooding the bowls on start up although the plugs seem very dry. I've stripped the carbs & cleaned them but to no avail. Any ideas?

The Boyer still needs 12v and the usual route is batt >ign sw >RH bar switch through the ign cut button and back to the coils and Boyer. Wire colour out of the headlamp from RH bar is White with blue tracer. Check if either end is live with ign on and non live off obviously. Can you trace the Boyer wiring? 12v is a white lead from Boyer. Only black and white is one of the Boyer leads to trigger plate in points cover. Check for continuity between the black coil wire and your detached black/white leads as I'd guess this is your problem. Popping and banging are usually electrical.

chiefdeal said:

After examining the wiring I found I had put a negative wire to a positive terminal on the coil on the side that was firing. Corrected this wire. Now both plugs sparking. Kicked for eternity with only backfiring from carbs & exhaust. Then lo & behold it started & ran for approximately 10 -15 seconds beautifully. It then just stopped running & no matter how many times I kick all I get is backfiring with the odd teaseing splutter.

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Are you certain all the Boyer connections are correct for (presumably?) positive earth? http://www.boyerbransden.com/instructions.html

Are you certain the ignition timing is set correctly?

To check, turn the crank to TDC with either cylinder on compression, then turn it backwards until the first visible alternator rotor mark lines up with 31 deg. BTDC on the timing scale, then check that the paint mark on one of the Boyer rotor magnets lines up with the upper timing hole in the pickup plate.

If the Boyer pickup wires have been reversed then that will throw the timing way off, and it won't advance.

Check all electrical connections thoroughly, the two wires to the pickup can break inside the insulation, and the soldered connections on the back of the pickup plate can also fail, both of these caused by engine vibration.

Try connecting the Boyer directly to the battery with jumper wires and see if the engine runs, as that will show up any faulty electrical connections in the wiring?

Bad connections inside the ignition switch and kill button can cause many problems.

Make sure you have a secure return wire connection between the engine and the frame and/or harness earth (Red) wiring back to the battery, as the Isolastics are quite effective at electrically isolating the engine from the frame and harness return wires.

The battery must be in good condition and reasonably well charged for a Boyer to run properly.

chiefdeal said:

I noticed a loose spade in a block (2'' x 3/4'' housed behind the steering head - this has 2 spades coming out of it of which 2 black & white wires connect to) which duly fell off. However, am I right in thinking that this block is part of the old ignition system & is no longer required as it has boyer ignition fitted?

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What you described sounds like the 2CP condenser pack (rubber block) which would have been connected to the original points wires (Black/White and Black/Yellow wires) , but certainly should not be connected to a Boyer system.
If you find a White ceramic block, that will be the ballast resistor, which must also be disconnected.

LAB/Kieth, thanksfor your responses. You were both right, it was an incorrectly wired boyer. Trying to remove the head & then re-install it resulted in me knocking out some connectors & putting them back in the wrong spades. A lesson learned. I phoned Les at Norvil & he talked me through the wiring while I was at the bike (this is a great service). After I'd wired it as he described, it started 1st kick! It has never ran as well as it does now.